Add a prelude emit mode to host/chez/emit.janet: when emitting clojure.core
itself (not user -e), a non-native clojure.core ref lowers to a runtime
var-deref instead of being rejected as out-of-subset, so core fns chain
through each other. Default (subset) mode is unchanged — the corpus probe
still rejects unimplemented core refs for a clean signal.
core-prelude-probe.janet walks the tiers through the live analyzer->emit
pipeline and catalogs reach + gaps (macros skipped; analyze-time only).
Baseline: 303/355 non-macro core forms emit. Remaining gaps are a tight
punch-list for the next increments: :throw (29), :quote (8), :try (2), Java
host interop (6), letfn (4), declare (2). Probe has a regression floor.
emit-test 83/83 (added prelude-mode lowering assertions); subset probe
619/619 unchanged; full gate green.
